The present invention relates to a method and apparatus for automating the construction of ships and more particularly to an apparatus for fabricating stiffener panel sections having webs and/or bulkheads utilizing automated laser welding equipment.
Since the early 1970's, a considerable effort has been made by the shipbuilding industry to improve productivity and reduce ship construction cost. A large part of this effort has been directed to the introduction in the shipyards of automated equipment and highly mechanized assembly line production systems where emphasis has been directed to precutting components, fabricating large subassemblies with the components and constructing the ship with the subassemblies using modular techniques. As much as eighteen percent of the total welding man-hours required during ship construction occurs in panel shops within the shipyards where shell sections of the ship are fabricated.
A typical panel shop includes, as a minimum, a plate delivery station, a manually operated tack welding station, a semi-automated butt welding station, a panel turnover station for two-sided welding, a manual marking and grinding station, a numerically controlled stiffener feed station, and a semi-automatic stiffener fillet welding station. Additionally, in most shipyard panel shops, stations are also included for manually mounting and welding webs and bulkheads to the panel. Typically, the majority of shipyards employ a one-sided welding method to obtain the butt welds. In recent years a number of shipyards have employed two-sided welding methods that incorporate gantry mounted, moderately high speed arc welders. Upon the completion of a butt weld on one side of a panel, the panel is turned over and the second side is butt welded, utilizing the same arc welders. This two-sided method permits higher production rates and results in lower cost for consumable electrodes than the one-sided method. However, due to the nature of the welds formed with conventional welding techniques, simultaneous two-sided welding of panels for ships has not been feasible using prior art techniques when the panel is in a horizontal position since the weld formed on the underside of the panel does not meet specifications due in part of the effect of gravity on the molten metal within the weld. Positioning the panel in a vertical position for two-sided welding is typically unfeasible due to the large cross-sectional area of the completed panel, typically fifty feet by fifty feet.